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21st April 2022
The risk of depression can be greatly reduced even by undertaking lower amounts of the recommended levels of physical activity according to the results of a meta-analysis by researchers from the MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Cambridge, UK.
Depression is a common, global mental disorder that is believed to affect 5% of the population. Moreover, a 2015 meta-analysis estimated that every year, 14.3% of global deaths, approximately 8 million deaths, can be linked to mental disorders. With such a high prevalence and associated mortality, much needs to be done to try and prevent or reduce depression risk. One possible mitigating factor is physical activity and according to one systematic review, promoting physical activity may serve as a valuable mental health promotion strategy in reducing the risk of developing depression. In fact, a 2018 meta-analysis of prospective cohort studies suggested that the available evidence supports the idea that physical activity can confer protection against the emergence of depression regardless of age and geographical region. With a good deal of evidence indicating a protective effect from physical activity, what remains uncertain is the strength or shape of the association between physical activity and depression.
For the present analysis, the UK team looked for trials that included any dimension of physical activity at three or more exposure levels, with at least 3,000 participants and with a follow-up period of not less than 3 years. Levels of physical activity were measured as marginal metabolic equivalents task hours per week (mMet-h/wk), where 1 Met represented the resting metabolic rate and 8.8 mMet-h/week was equivalent to the recommended weekly amount of physical activity. The outcome of interest was depression, major depressive disorder and elevated depression symptoms.
Depression risk and physical activity levels
The literature review identified 15 eligible publications including 191,130 participants (64% women) contributing 28,806 incident depression events and 2,110,588 person-years.
The results suggested an inverse and curvilinear dose-response between physical activity and depression, such that relative to adults who did not report undertaking any physical activity, those doing at least half of the recommended activity (4.4 mMet-hrs/week), had an 18% lower risk of depression (relative risk, RR = 0.82, 95% CI 0.77 – 0.87). Among those achieving the recommended amounts of activity (8.8 mMet-hrs/week), there was a 25% reduced risk of depression (RR = 0.75, 95% CI 0.68 – 0.82) and this reduction was the same for major depression and slightly lower for elevated depressive symptoms (RR = 0.73). However, interestingly, there was little apparent benefit derived from increasing activity to 17.5 mMet-hrs/week (RR = 0.72, 95% CI 0.64 – 0.81), for each of the three outcome measures.
Using potential impact fraction (PIF) analysis, the authors calculated that around 11.5% of incident depression could have been prevented in adults who achieved at least 8.8 mMet-hrs/week of physical activity.
Translating their findings into practical advice, the authors stated that accumulating an activity equivalent to 2.5 hours/week of brisk walking was associated with a 25% lower risk of depression and that achieving half of this level, reduced the risk by 18% compared with those who undertook no physical activity.
They concluded that substantial mental health benefits accrue from the achievement of physical activity levels even below those currently recommended.
Pearce M et al. Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis JAMA Psychiatry 2022